Conventional optical projection lithography has been the standard silicon patterning technology in semiconductor manufacturing processes, e.g., in integrated circuits (ICs) fabrication. During the lithographic projection, a mask that includes a semiconductor circuit layout pattern can be imaged onto a substrate that is at least partially covered by a layer of photoresist (i.e., “resist”). Layouts used to create such masks are typically generated using computer-aided design (CAD) programs, sometimes called electronic design automation (EDA). For example, most CAD programs follow a set of predetermined design rules in order to create functional masks.
One goal in IC fabrication is to faithfully reproduce the original circuit design or layout on the wafer using the designed mask. Another goal is to use as much of the wafer real estate as possible. As the size of an IC is reduced and its density increases, however, the critical dimension (CD) of its corresponding mask approaches the resolution limit of the optical exposure tool. For example, transistor matching requirements for advanced technology nodes, such as less than 1.0 μm, require exquisite CD control, beyond the capability of current lithography and etch tools and processes. An important component of variation is matching between gates in the interior of an array of active gates, e.g., over the same active region, and those on the end of the array. For example, for the 45 nm technology node, the printed interior gates may vary from their designed size by a value of X, while the printed end gates might vary from their designed size by a value of 2 to 3 times X.
Dummy polysilicon is often used to reduce feature variation, e.g., for gates at the end of a gate array. In order to avoid dummy gates interfering with the device performance, dummy gates must be formed far away from the active gates. Additionally, to reduce interference of the dummy polysilicon feature on the “live” feature, the dummy feature should be spaced from the live feature by some minimum amount.